1. Field of the Invention
This invention relates to methods and apparatus for detecting distortion in an output signal which a signal handling means (such as an amplifier) produces in response to an input signal.
2. Description of the Related Art
It is known to use distortion reduction mechanisms on amplifiers in an attempt to linearise the amplifier's response. It is often desirable to monitor residual distortion in the output of the amplifier, and to use this signal to adapt the distortion reduction mechanism to maximise the cancellation of the distortion. It is known to use a pilot signal to detect residual distortion. The pilot signal is added to the input signal and detected in the output signal so that any distortion it experiences can be assessed. The use of pilot signals for distortion detection has the disadvantage that a pilot signal must be generated, detected and then removed from the output signal afterwards. Thus, the use of pilot signals increases system complexity and adds the risk that spurious noise or continuous wave (CW) emissions introduced by the pilot signal detection system will remain as unwanted residues in the amplifier output.